2 Plywood Versatile building material. Plywood made into foundation forms, provides stiff uniform surface for forming concrete.Plywood floor, wall & roof sheathing stiffens & strengthens structure of the house.Plywood used for soffits provides a smooth, easy-to-paint surface.As underlayment, plywood makes a smooth substrate for finish flooring.When used in cabinets & built-ins, is relatively light but very strong. Holds fasteners well & can use various types of joinery.
3 Plywood Basics Traditionally divided into two categories: Softwood Plywood -construction & industrialHardwood Plywood – used for paneling, cabinets, built-ins, & other interior features.
4 Structure of PlywoodConsists of layers of wood veneer that have been glued together. Called plies.Manufactured with an odd number of layers. Grains run opposite of previous layer.Construction & industrial may have three, five or seven layers.Outermost grain plies always run in same direction. Usually along the length of the panel.Outermost plies are called face plies. Best quality is front face, other is back face. Plies between are called the core.Hardwood plywood may be entirely veneer or veneer bonded to core of glued-up lumber. Called lumber-core plywood.Hardwood plywood may also have particleboard core. Particleboard is made of very small particles of wood bonded together.
5 Plywood Manufacturing Logs go into a pond for storage. Only select logs (peeler logs) will have veneer cut from them.Passes through debarker - uses high pressure jets of water to blast off bark.Stripped log is chucked into a lathe. Spun against a long, razor, sharp steel blade. Slices a continuous strip of thin wood veneer from the log. Like paper towels being unwound from a roll.Moves over conveyors to clipping machine. Cut to specific width with giant knives.Passed into dryers. Moisture content removed to provide stability & better glue bond.Natural defects cut out & filled with solid lumber or synthetic patching material.
6 Plywood Manufacturing continued Then go through glue-spreader. Both sides spread with adhesive. Glue covered sheets are stacked alternately with unglued sheets to make panels of desired thickness. Called the lay-up process.After lay-up panels go into presses that bond wood & glue together using pressure and sometimes heat. Result is highly durable bond.Creates a product that is strong, rigid, dimensionally stable, and able to resist great impact.Panels trimmed to exact width & length. Sanded slightly to final thickness & inspected. Blemishes in face plies are repaired.Panels graded & bundled for shipping.
7 Classifying Plywoods Construction plywoods are graded. Grade marks stamped on face of all plywood that meets APA (Engineered Wood Association) standardsPurpose is to identify all features of a panel. Enables builders to select right panel for the job & building inspectors can verify correct materials have been used.Characteristics that affect grade:Type of adhesives usedVeneer qualityWood SpeciesConstructionSizePerformanceSpecial Characteristics.
8 Classifying Plywoods continued Adhesives – Type of adhesive used affects panel’s resistance to weathering & moisture.Exterior panels designed for full & continuous exposure to weather made with water-resistant glue.Interior panels made with glues not water resistant. Should be used indoors only.
9 Classifying Plywoods continued Veneer Quality – Specified by a letter designation ranging from A (highest) to D (lowest)Plywood often has face plies of differing quality. E.g. Cabinet plywood labeled A-C has one face of high quality veneer and the other of lower quality.Mixing veneers allow mills to conserve quality woods & produce panels more cost effectively.
10 Classifying Plywoods continued Wood SpeciesMost construction plywoods made of softwoods such as Douglas fir.Species divided into five groups. Strongest woods found in Group 1. (p.330)ConstructionNumber of layers in a panel usually same as number of plies.Sometimes inner plies may be glued together with grain running parallel, forming single inner layer.SizeThickness of standard plywood ranges from ¼” – 1 ¼” or more.Commonly available in panels 4’ wide & 8’ to 12’ long. Most common size in residential construction is 4’ x 8’
11 Classifying Plywoods continued PerformanceSome designed for special engineering uses where strength & stiffness are of maximum importance. Structural PanelsImportant to select correct sheathing for each construction need.Special CharacteristicsOften adapted for special uses. E.g. foundation grade plywood treated with preservative chemicals.Used where wood will permanently be installed in contact with earth.Tongue-and-groove plywood used in construction of single layer flooring systems.
12 Classifying Plywoods continued Hardwood plywoods classified by face-ply arrangements.More expensive than construction plywood.Commonly 4’ x 8’ x 3/4” sheets.Birch, Maple & Oak most frequently used. Other domestic & exotic woods available.Used for finish work where appearance is important.
13 Classifying Plywoods continued Four basic milling methods of hardwood plywood:Rotary cutting – Log mounted & turned on lathe % of veneer cut this way.Plain or Flat Slicing – Half log mounted with heart side flat against guide plate of slicer.Half-Round slicing – Log segments mounted off center in lathe. Often used on red & white oak.Rift cutting – obtained by cutting perpendicularly to medullary rays either on lathe or slicer.
14 Working with Plywood Storage Cutting Store flat whenever possible – Reduces chances of warpingStore indoors until ready for use or protect from weather with waterproof tarp. Stack on spacers at least 1 ½” above ground.CuttingSupport firmly on each side of cut line to prevent binding & kickback when cutting.Cutting with hand-held circular saw best face should be down to minimize splinteringCutting with table saw best face should be up to minimize splintering.Blade teeth should just clear top of plywood.Scoring veneer with utility knife also helps reduce splintering.
15 Working with Plywood continued ShapingMay be shaped like solid lumber. Do not sand faces too much it is only a thin layer of veneer.FasteningMay be fastened to other materials using wood adhesives, nails, & screws.No fastener works as well on edges as it does on face plies. Important when attaching hinges.Pre-drilling helps prevent splitting when driving screws. Screws with sharp points (drywall & decking screws) may be driven without pre-drilling.When nails or screws are not enough to hold in place adhesive should be used as well. Called glue-nailing. Produces a strong bond.Where finish nails are used nail holes should be concealed with wood putty. When using screws countersink so heads are flush with surface of plywood.
16 Check Your KnowledgeName at least three general uses for plywood in residential building construction.Describe the arrangement of plies in a typical sheet of plywood.Describe the technique used to minimize splintering when cutting plywood.
17 Composite Panel Products Made from pieces of wood mixed with adhesive.Used for sheathing, subflooring, cabinetry & paneling.Most common types:Oriented-strand board (OSB)HardboardMedium-Density Fiberboard (MDF)Particleboard
18 Composite Panel Basics Often made from wood that would otherwise be unused or wasted.Trees not appropriate for veneers.Trees too small for lumber production.Trees that grow too quickly to produce sound lumberPortions of trees that would go unused, such as stumps & limbs.
19 Structure of Composites Wood pieces range in size from small fibers to large flakes.Two strong influences on properties of composite panels are:Size & shape of individual flakes & particlesRatio of adhesive to particles
20 AdhesivesCritical ingredient of composite panels, used to bond wood pieces & particles.Phenol-formaldehyde adhesives used for exterior structural panelsWater-resistantUrea-formaldehyde adhesives used for indoor use panelsVery smooth surface
21 AdditivesOther ingredients may be added to mix to change characteristics of panelsWax added to reduce tendency to absorb moistureFire retardant makes more suited for wildfire areasPreservatives make panels last longer
22 Composite Panel Manufacturing Logs or wood scraps processed to create fairly, small uniform pieces.Pieces mixed with adhesives & other additivesMixture then formed into thick mat.Mat is squeezed under heat & pressure into sheets of specified thicknessHeat & pressure released when adhesive has cured.
23 Composite Panels – Special Finishes Composite panels can be given special finishes at mill.Surfaces may be filled or primed for easy painting, embossed or textured for decorative surfaces, covered with vinyl overlayEdges may be banded with lumber, machined for tongue-and-groove joints, or given special sanding or overlays.Panels can be laminated together to make unusually thick panels.Also glued together to make unusually large panels
24 The Future of Composites Each new product tested before it’s approved for construction use.Many composites incorporate chemicals and other additives.Important to learn about new products before using (info about long-term structural performance & impact on environment & human health) Review MSDSAlways wear duct mask to protect from inhaling potentially harmful dust from adhesives.
25 Working with Composites Composites are free from cracks & imperfections. Can be worked with standard woodworking tools.All types of joints can be madeArchitectural panels may be butted or splined.Absence of voids gives products a full, uniform contact surface for gluing.
26 Oriented-strand board Made from wood strands bonded with adhesive under heat & pressure.Strands in each layer positioned so they run in one direction. Then layers placed perpendicular to each other. Usually have three or five layers.Available with square or tongue-and-groove edges.Thicknesses range from 3/8” – 1 1/8”Not suited to long-term exposure to weather.Will shrink and swell slightly with humidity changesShould be installed with 1/8” gap between ends and ¼” at sides.Panels should be stacked off ground & metal straps holding panels should be cut right away to prevent damage to edges if swelling occurs
27 Fiberboard Includes hardboard & medium-density fiberboard. Logs chipped into small pieces then reduced to fibers by steam or mechanical processes.Fibers refined & mixed with adhesive.Compressed under heat & pressure to produce panels.Will not split, crack, or splinterDense with extremely smooth front & back surfaces – superior wear resistance
28 HardboardHigh-density fiberboard used for interior paneling, flooring underlayment, & cabinet back panelsStandard has high strength & good water resistance. Very smooth surface, used in cabinetwork.Tempered has linseed or tung oil added before pressing. Improves stiffness, scratch & water resistance.Manufactured with one or both sides smooth. One side is S1S, two sides is S2S.Available in thicknesses 1/8” – 3/8”.Perforated hardboard has very closely spaced holes punched or drilled into it. Holes can be fitted with metal hooks, holders, supports, etc.
29 Medium-Density Fiberboard Have uniform thickness & extremely smooth surface.Ideal where end product will be paintedImportant to wear dust mask when cutting or sanding to avoid breathing fine dust particles.Also very dense & heavy. Take care when handling & lifting.
30 ParticleboardUsed indoors where a smooth & relatively inexpensive surface is requiredRarely used as finish surface.May be used as substrate for laminate countertops, floor underlayment.Not as strong as MDF & OSBThickness ¼” – 1 ½”
31 Fiber-Cement BoardMade of cellulose fibers bonded together with mixture of Portland cement, ground sand, additives, & water.Considered non-combustible & rot proof.Standard panel is 5/16” thick & very denseOne side smooth, other side rougher.Smooth finish & stability make very desirable for siding.
32 Handling & Cutting Fiber-Cement Board Store under cover on dry, level surfacePanels are thin, flexible & heavy. Should be carried on edge by two people.May be cut with special shears, but carbide-tipped circular saw blades are used more.Fiber-cement contains silica. Where a dust mask to prevent silicosis.
33 Check Your KnowledgeHow does a composite panel differ from a plywood panel?What is the purpose of adding wax to a composite panel during manufacture?Name the two types of fiberboard.Where is fiber-cement board used?